Trajan enlarged the basin, and in a short time there grew around it a city which eventually became independent of Ostia.

In 849 Pope Leo IV fortified it and established there a colony of Corsicans for the defence of the coast and the neighbouring territory, but the city continued to decay.

[5] In 682, it is recorded that Pope Leo II was consecrated by the bishops of Ostia, Porto and Velletri (the See of Albano being vacant).

[7] On 1 August 1018, Pope Benedict VIII confirmed for Bishop Benedictus all the possessions of the church of Porto, which were named in detail and included not only the entire city of Porto, but also the Isola Lycaonia and the island with the church of S. Bartholomew, and the Transtiberine region of Rome; the grant included the complete rights over people's estates who died in his jurisdiction without an heir, or intestate, or involved in a legal situation.

[9] Cære was an ancient city, called at first Agylla, where the sanctuaries of Rome and the Vestals were hidden during the invasion of the Gauls; the Etruscan tombs scattered about its territory are important archeologically.

Rufina and Secunda on the Via Aurelia, fourteen miles (21 km) from Rome; the basilica is said to have been begun by Pope Julius I, and was finished by Saint Damasus.

[13] In November 1037, Bishop Petrus and all his successors were granted the office of Bibliothecarius (Librarian) of the Holy Roman Church.

In 1826, Civitavecchia was separated from the Diocese of Viterbo and Toscanella and united with that of Porto, by Pope Leo XII.

[22] By the beginning of the 20th century, it had become apparent that the suburbicarian bishops had become overburdened with the responsibilities of their curial and diocesan duties.

Pope Pius X issued a decree, Apostolicae Romanorum Pontificium, granting the bishops of Ostia, Porto, Albano.

The decree also ordered that the bishop of Ostia, when promoted to that position, should also retain his previous bishopric; the diocese of Velitrae was to be removed from his jurisdiction, and from that point the suburbicarin bishops would be: Ostiensis, Portuensis et Sanctae Rufinae, Albanensis, Praenestina, Sabinensis, Tusculana, Veliterna.